There is a related technology using, as a cache of a storage system, an SSD (Solid State Drive) on which a non-volatile semiconductor memory, such as a NAND flash memory, is mounted. For example, the data in a disk device on a network is cached in an SSD in a server device to which an access faster than that to the disk device can be made. Improvements in accessibility are made by using, as tag information, information on the storage location and the data size of the cached data.
Furthermore, for example, data is cached in the SSD and a control program causes the tag information on all the cached data to be stored in the memory in the server device. With reference to the tag information stored in the memory, it is determined whether there is the cached data or not.
Patent Document 1: Japanese Laid-open Patent Publication No. 10-040170
Patent Document 2: Japanese Laid-open Patent Publication No. 2003-223284
However, the related technology has a problem in that it is not possible to increase the accessibility while reducing the memory usage. For example, the related technology stores the tag information on all the data cached in the SSD in the memory, which increases the memory usage.
Furthermore, for example, for the related technology, a mode can be assumed where the tag information on the cached data is not stored in the memory and an access to the SSD is made to determine whether there is the cached data or not. In this case, while the memory usage can be reduced, an access to the SSD is made each time an access to the data occurs. If there is not the data cached in the SSD, an access is made to the data stored in the disk device; however, in this case, an access to the SSD occurs before the access to the disk device, which lowers the data accessibility. As described above, it is difficult for the related technology to increase the data accessibility while reducing the memory usage.